reset import hook on shutdown
Fix Jira issue #ROOT-6191: TBrowser and canvas editor

Embed the Pad Editor in the left tab of the browser instead of in the canvas itself, as suggested by Axel in the Jira issue #ROOT-6191
Fix Jira issue #ROOT-6221: Text editor does not allow negative positions

Apply patch kindly sent by Matthew Strait
Unanamed macros not detecting leading and trailing comments. (ROOT-5930 and ROOT-4791).
Multiple line of leading comments. (ROOT-5930 and ROOT-4791).
Only complain about inspecting std classes for persistent members.
Give libCling an extension.
Fix warning on Windows
Fix warnings on windows
Extract the interpreter from TCling.
Detect TCling construction from rootcling.
rootcling brings its own libCling, no need to dlopen it.
Rename ROOTBUILD to ROOT_STAGE1_BUILD; ROOT will specify -rootbuild for stage2.

rootcint_tmp will be used for libCore and libRIO; rootcint will generate all
subsequent dictionaries. ROOT will pass "-rootbuild" as argument to signal that
rootcling is invoked for building ROOT.
Add more rootcling interpreter flags.
Add extern "C" layer between TCling (rtti) and rootcling (no-rtti).
Also define resourcedir for TCling interpreter.
Rename vars from CINT to CLING. rootcling_tmp only used for libCore,RIO.

rootcling will write out ROOT files; that does not work for libCore and RIO
which instead use rootcling_tmp.
All other libraries use rootcling -rootbuild.
Rename ROOTCLINGTMP to ROOTCLINGSTAGE1; rootcling -rootbuild is ROOTCLINGSTAGE2.
Trigger TROOT::TROOT() and friends.
rootcling must not load the PCH.
Rename $(ROOTCLINGTMP) to $(ROOTCLINGSTAGE1); utils depends on system.